Multiple speed hydraulic drive circuit

ABSTRACT

THE DISCLOSURE CONCERNS A HYDRAULIC POWER CIRCUIT PARTICULARLY SUITED FOR USE IN DRIVING THE ELEVATOR OF AN EARTH-MOVING SCRAPER, AND WHICH AFFORDS THREE DRIVING SPEEDS IN THE FORWARD DIRECTION AND ONE DRIVING SPEED IN REVERSE. THE CIRCUIT PREFERABLY EMPLOYS TWO FIXED DISPLACEMENT PUMPS OF DIFFERENT CAPACITIES, AND A PAIR OF PILOT OPERATED CONTROL VALVES WHICH SELECTIVELY CAUSE THE OUTPUT OF EITHER OR BOTH PUMPS TO BE DELIVERED TO THE DRIVE MOTOR. THE CONTROL VALVES ARE SO ARRANGED THAT THEY MAY BE INCORPORATED IN A SINGLE, CONVENTIONAL VALVE BODY, AND THAT NEITHER HAS TO BE SIZED TO HANDLE THE COMBINED OUTPUTS OF BOTH PUMPS.

United States Patent [191 [111 3,835,647

Huffman Sept. 17, 1974 1 MULTIPLE SPEED HYDRAULIC DRIVE CIRCUIT Primary ExaminerEd ar W. Geo he an E 8 b [75] Inventor: Theron M. Huffman, Paw Paw, Attorney, Agent, or Firm-Jeffrey S. Mednick Mich. [73] Assignee: General Signal Corporation, [57] ABSTRACT e 180 osure concerns a rau no power circuit ar- Rochester, NY. Th d. l hyd l' p ticularly suited for use in driving the elevator of an P116411 1972 earth-moving scraper, and which affords three driving [21] Appl NO; 221,343 speeds in the forward direction and one driving speed in reverse. The circuit preferably employs two fixed displacement pumps of different capacities, and a pair [52] US. Cl 60/486, 91/6, 60/493 f pilot Operated comm] valves which Selectively [51] Int. Cl. Fl5b 15/18 cause the output of either or both pumps to be deliv Field of Search 60/52 R, 52 HE; 91/6 ered to the drive motor. The control valves are so arranged that they may be incorporated in a single, con- References Cited ventional valve body, and that neither has to be sized UNITED STATES PATENTS to handle the combined outputs of both pumps.

2,874,682 2/1959 Vanderkaay 60/52 S X 10 Claims 4 Drawing Figures 2,879,612 3/1959 Schultz et al.... 60/52 HE 3,360,925 1/1968 Zimmerman 60/19 3,443,380 5/1969 Karazisa 60/52 HE CON STAN T PRES SURE UQCE 34 PATENTEB SEPI 71974 sum 1 or 2' MULTIPLE SPEED HYDRAULIC DRIVE CIRCUIT BACKGROUND AND SUMMARY OF THE INVENTION Although it is common practice to use a hydraulic drive for the elevator of a self-loading, earth-moving scraper, each of the prior drive circuit proposals of which I am aware has disadvantages which limit its utility. The simplest circuit includes a single fixed displacement pump, and a two-position selector valve which either unloads the pump or delivers its output to the drive motor. This arrangement affords only a single driving speed; therefore, the elevator operates efficiently only in a very limited range of vehicle speeds. Moreover, since the driving direction cannot be reversed, dislodgment of objects caught in the elevator can be difficult.

These disadvantages have given rise to several propos- 'als for improving the performance of the basic circuit. One of these involves the addition of a directional control valve which allows reversal of the direction of flow through the motor. Another consists in the addition of a second fixed displacement pump which is selectively unloaded or connected in parallel with the main pump by a selector valve. This auxiliary pump may serve only the drive circuit, in which case its output. always is available for driving purposes, or it may be an implement pump whose output is conveyed to the drive circuit through a high pressure carry-over in the implement control valve, and thus is available only when the implements are idle. While these proposals provide an effective solution of the dislodgment problem and do increase the range of vehicle speeds in which efficient elevator operation can be achieved, they do not accommodate the wide range of ground speeds which are encountered in some applications. Moreover, if the twopump drive incorporates a directional control valve, that valve must be sized to handle the combined outputs of both pumps. This increases the cost of the circuit.

Another prior drive circuit, and probably the best in certain applications, consists of a hydrostatic transmission using a fixed displacement piston motor and a variable displacement, overcenter piston pump. This proposal affords reversing capability as well as infinitely variable drive speed, and thus constitutes a very attractive solution to the drive problem in applications where its cost is comparable to that of the dual pumpreversing valve scheme. Unfortunately, at the present time, transmission pumps and motors are mass produced, and thus readily available on the commercial market, only in capacities up to about 6 cubic inches per revolution, which is the size required 16 satisfy the power requirements of the elevator on a 9 cubic yard scraper. Since the cost of larger transmission components increases at a rate far exceeding that normally attributable to the change in power rating, this type of drive is impractical for large scrapers, particularly those in the 20-40 cubic yard class.

The object of this invention is to provide an improved hydraulic drive circuit which accommodates a wider range of ground speeds than the prior proposals which employ fixed displacement pumps, and which is more economical than the hydrostatic tansmission proposal in the sizes required for high power applications. According to the invention, the new circuit includes a drive motor which is selectively supplied with the output of either or both of a pair of fixed displacement pumps depending upon the positions of a pair of control valves. The pumps have different capacities, so the circuit affords a choice of three driving speeds. One of the pumps is connected with the motor through a check valve and is selectively loaded and unloaded by one of the control valves, which also is arranged to selectively open and close a return path leading from the motor. The second valve, on the other hand, controls a supply path from the other pump to the motor as well as an additional return path from the motor to a fluid reservoir. With this arrangement, neither control valve is required to handle the combined outputs of the two pumps, and both valves can be incorporated in a conventional tandem (i.e., series-parallel circuit) valve body having the usual Y-shaped coring for the open center path. These features contribute to the relatively low cost of the circuit.

In its preferred form, the drive motor is reversible, and the second control valve takes the form of a conventional three-position directional control valve which is adapted to reverse the direction of flow through the motor. Moreover, in this version of the invention, both control valves are of the pilot operated type and are operated by a remote control system having a single actuating lever which determines the positions of both control valves. This embodiment, therefore, facilitates dislodgment of objects stuck in the elevator, reduces operator effort, and allows considerable freedom in locating and arranging circuit components.

BRIEF DESCRIPTION OF THE DRAWINGS The preferred embodiment of the invention is described herein with reference to the accompanying drawings in which:

FIG. 1 is a schematic diagram of the improved drive circuit.

FIG. 2 is a sectional view taken on line 22 of FIG.

FIG. 3 is a sectional view taken on line 3-3 of FIG.

FIG. 4 is a cross sectional view of the control valve assembly used in the FIG. 1 circuit.

DESCRIPTION OF ILLUSTRATED EMBODIMENT As shown in FIG. 1, the drive circuit includes a reversible, rotary hydraulic motor 11 which drives the elevator (not shown), a pair of engine-driven, fixed displacement pumps 12 and 13 of unequal capacities, and a fluid reservoir or tank 14. Motor 11 is provided with a pair of ports Ila and 11b, either of which may serve as the supply port while the other serves as the return port, and which are connected to the service lines 15 and 16, respectively. These lines are equipped with criss cross relief valves 17 and 17a which serve to prevent cavitation and reduce shocks when motor 11 is stopped or reversed.

The smaller supply pump 12 is connected with service line 15 through a conduit 18 containing a check valve 19, and is selectively loaded and unloaded by a two-position control valve 21 which is connected with conduit 18 at a point upstream of the check valve via branch conduit 22. In addition to its unloading function, valve 21 also controls a motor return path leading from service line 16 to tank 14 through conduit 23. Valve 21 is biased by spring 24 to the illustrated position, in which it unloads pump 12 and closes conduit 23, and is shifted to the second position, in which it loads pump 12 and opens conduit 23, by a piloted pressure motor 25 which is actuated by a remote control system 26.

The larger supply pump 13 is selectively unloaded, or loaded and connected with one or the other of the service lines 15 and 16, by a three-position control valve 27 which also is adapted to establish a return path from the remaining service line to tank 14. Valve 27' is biased to the illustrated neutral position by a pair of centering springs 28 and 29 and is shifted to one or the other of two motor-actuating positions by a pair of opposed piloted pressure motors 31 and 32 under the control of system 26. In its neutral position, valve 27 unloads pump 13 to tank 14 and isolates the service lines 15 and 16 from both of these components and from each other, whereas in each of the actuating positions the unloading path is closed, one service line is connected to pump 13, and the other service line is connected to tank l4.

It should be noted here that, while valve 27 is connected with pump 13 through control valve 21, this path is continuously open. Therefore, the functions of valve 27 are not affected by actuation of valve 21.

The remote control system 26 comprises a pilot valve 33 which is supplied with hydraulic fluid at a relatively low, constant pressure on the order of 250 psi. by a source 34, such as the power steering circuit of the vehicle, and which contains a pair of valving units 35 and 35a which serve to pressurize and vent the piloted pressure motors of control valves 21 and 27, respectively, in accordance with the position of a common actuating lever 36. Valve unit 35 includes a spool 37 which is equipped with a conventional centering spring and detent assembly 38, and which is formed with a land 39 which controls communication between an outlet chamber 41, which is joined to piloted motor 25, and supply and exhaust chambers 42 and 43, respectively. When spool 37 is in the illustrated neutral position, toward which it is biased by the centering spring, land 39 blocks communication between chambers 41 and 42, and the outlet chamber is in free communication with exhaust chamber 43. On the other hand, when spool 37 is shifted to the left to the detented actuating position, land 39 blocks communication between chambers 41 and 43, and the outlet chamber is connected with supply chamber 42. Valve unit 35 is a double-acting unit, so spool 37 includes another land 44 which controls communication between a second outlet chamber 45 and the supply and exhaust chambers 42 and 46. However, since control valve 21 incorporates only a single actuating motor, this added capability of unit 35 is not needed, and the outlet port of chamber 45 is sealed by a plug 47.

Valve unit 35a is identical to unit 35, but its full double-acting capability is needed. Therefore, outlet chamber 41a is connected with piloted motor 31, outlet chamber 45a is connected with opposed motor 32, and the second detented actuating position of spool 37a (i.e., the position of the right of neutral) is utilized.

The spools 37 and 37a of the two pilot valve units are shifted by the common actuating lever 36 which includes a plate 49 containing a pair of aligned slots 51 and 51a in which the spherical heads 52 and 52a of the spools are held captive. Plate 49 also is provided with a third slot 53 in which is retained the spherical head 54 of a fixed pivot 55. Lever 36 is biased to the illustrated neutral position, in which it is parallel with spools 37 and 37a, by the centering springs associated with those spools, and can be tilted about fixed pivot head 54 to one of the following four actuating positions labeled in FIG. 2:

a. Low Speed Position L in which it shifts spool 37 to its actuating position, to thereby pressurize chamber 41, but keeps spool 37a in neutral position.

b. Medium Speed Position M in which it shifts spool 37a to its first actuating position, to thereby pressurize chamber 41a and vent chamber 45a, but keeps spool 37 in neutral position.

c. Fast Speed Position F in which it shifts both of the spools 37 and 37a to the actuating positions just mentioned.

(1. Reverse Position R in which it shifts spool 37a to its second actuating position, to thereby pressurize chamber 450 and vent chamber 41a, but keeps spool 37 in neutral position.

When the illustrated circuit is in service and lever 36 is in the neutral position, the outlet chambers 41, 41a and 45a of the pilot valve 33 are in free communication with tank 14 through the associated exhaust chambers 43, 43a and 46a. Therefore, the three piloted motors 25, 31 and 32 are vented, and the springs 24, 28 and 29 hold the control valves 21 and 27 in their neutral positions. As a result, both of the pumps 12 and 13 are unloaded to tank 14, and drive motor 11 is hydraulically locked.

In order to drive the elevator in the forward direction at the lowest of the three available speeds, lever 36 is tilted to position L. This action raises the pressure in pilot valve outlet chamber 41 and in the connected piloted motor 25, so the latter now shifts control valve 21 to its second position to thereby load the small pump 12 and open a return path for motor port 11!). The output of pump 12 is now delivered to motor 11 via conduit 18, check valve 19, service line 15 and port 11a, and the fluid exhausting from port 11b is returned to tank 14 via service line 16 and return conduit 23. Therefore, motor 11 will now drive the elevator at a low speed proportional to the delivery rate of pump 12.

If lever 36 is tilted to position M, pilot spool 37 will return to the illustrated neutral position under the action of its centering spring to thereby again vent piloted motor 25 and allow spring 24 to return control valve 2 to its neutral position. This action unloads pump 12 and closes return conduit 23. Simultaneously, pilot spool 37a is shifted to its first actuating position, so outlet chamber 41a and piloted motor 31 are pressurized by source 34, and chamber 45a and motor 32 remain vented. Therefore, motor 31 will shift control valve 27 to the actuating position in which it connects pump 13 with service line 15, and opens a return path from service line 16 to tank 14. Since the check valve 19 prevents the escape of oil from line 15 through the unload ing path established by valve 21, the full output of large pump 13 will be delivered to motor 11, and the latter will now drive the elevator at a higher speed.

The highest output speed of motor 11 is developed by shifting lever 36 to position F. in this mode of operation, the pilot valve outlet chambers 41 and 410 are pressurized, so piloted motors 25 and 31 set both of the control valves 21 and 27, respectively, to their second positions. As a result, both of the pumps 12 and 13 are loaded, and their combined outputs are delivered to motor 11. In contrast to the previous modes of operation, the return flow from motor 11 is delivered to tank 14 along two parallel paths; one leading through conduit 23 and control valve 21, and the other leading through control valve 27. Inasmuch as the flow rate through motor 11 now equals the sum of the outputs of the two pumps, the driving speed will equal the sum of the low and medium speeds.

In the event it becomes necessary to reverse the elevator, lever 36 is shifted to position R. This movement of the actuator allows spool 37 to return to its neutral position, thereby causing control valve 21 to unload pump 12 and block return conduit 23, and simultaneously shifts spool 37a to the right to the second actuating position in which it isolates outlet chamber 45a from exhaust chamber 46a and opens communication between the outlet chamber and supply chamber 420. Since piloted motors 31 and 32 are now vented and pressurized, respectively, control valve 27 is moved to the left to the position in which large pump 13 is connected with service line 16, and service line is connected with tank 14. Inasmuch as these connections reverse the direction of flow through motor 11, the motor now drives the elevator in reverse. Its speed, of course, is proportional to the output of pump 13, and thus is the same as during forward operation at medium speed.

In the preferred form of the invention, the two control valves 21 and 27 take the form of sliding plunger valves, and, together with the relief valve 56 for large pump 13, they are incorporated in the conventional tandem circuit valve body 57 shown in FIG. 4. The body 57 is cored to provide a C-shaped exhaust manifold 58, which communicates with an exhaust port 59 and has legs 61 and 62 which interconnect the annular chambers 63-66 located at opposite ends of the plunger bores 67 and 68. The body also is cored to provide a central unloading path which includes a yshaped section 69 leading from inlet port 71 to the annular chambers 72 and 73 encircling bore 67, a second y-shaped section 74 connecting the central annular chamber 75 of bore 67 with the annular chambers 76 and 77 encircling bore 68, and a downstream portion 78 leading from the central chamber 79 of bore 68 to the exhaust manifold. Each valve bore is also provided with a pair of annular outlet chambers 81, 82 or 83, 84 which communicate with service ports 81a, 82a, 83a and 84a, respectively; the ports 81a and 82a being connected to branch conduit 22 and return conduit 23, respectively, and the ports 83a and 84a being connected with service lines 15 and 16, respectively.

The control valve 21 of FIG. 4 includes a solid valve plunger 85 formed with three axially spaced peripheral grooves 86-88 which define four valve lands 89, 91, 92 and 93, and is biased by a pair of springs 24 to the illus-' trated neutral position in which groove 86 interconnects chambers 63' and 81, and lands 92 and 93 isolate outlet chamber 82. Plunger 85 is moved to its second or actuating position by the piloted motor 25, which includes the left end of the plunger, and in this position lands 89 and 91 isolate outlet chamber 81, and groove 88 interconnects chambers 64 and 82. In both positions of valve 21, groove 87 interconnects chambers 72, 73 and 75, so control valve 27 always is able to receive oil from pump 13 via inlet port 71 and the open center path regardless of the position of valve plunger 85.

The preferred control valve 27, on the other hand, includes a conventional threeposition hollow valve plunger 94 formed with three lands 95, 96 and 97 which are separated by a pair of peripheral grooves or necks 98 and 99. The plunger contains two axial bores 101 and 102, each of which is intersected by a pair of axially spaced radial passages 103 and 104 or 105 and 106. The arrangement of the parts is such that e a. in the illustrated neutral position, lands and 97 isolate outlet chambers 83 and 84, and plunger necks 98 and 99 connect chamber 79 with chambers 76 and 77, respectively, and thereby complete the open center unloading path;

b. in the second position, to which the plunger is moved by motor 31, lands 95 and 96 close the open center path, radial passages 103 and 104 register, respectively, with chambers 83 and 76, and radial passages and 106 register, respectively, with chambers 66 and 84', and

c. in the third position, to which the plunger is moved by motor 32, lands 96 and 97 close the open center unloading path, radial passages 103 and 104 register, respectively, with chambers 65 and 83, and radial passages 105 and 106 register, respectively, with chambers 84 and 77.

I claim 1. A hydraulic drive circuit comprising a. a hydraulic motor (11) having first and second ports (11a, 11b);

b. a fluid reservoir (14);

c. a pair of pumps (12, 13) connected to draw fluid from the reservoir and discharge same under pressure;

d. conduit means (18) connecting the first pump (12) with the first motor port (11a);

e. means preventing reverse flow from the first port (110) through the conduit means;

f. a first control valve (21) connected with the first pump (12), the second motor port (110) and the reservoir (14) and having a neutral position in which it unloads the first pump to the reservoir and isolates the second motor port from both of these components, and a second position in which it closes the unloading path and connects the second motor port with the reservoir; and

g., a second control valve (27) connected with the second pump (13), the reservoir (14) and the motor ports (11a, 11b) and having a neutral position in which it unloads the second pump to the reservoir and isolates the motor ports from both of these components, and a second position in which it closes the unloading path and connects the first (11a) and second (11b) motor ports with the second pump and reservoir, respectively.

2. A drive circuit as defined in claim 1 in which a. the pumps (12, 13) are fixed displacement pumps having different capacities; and

b. the means for preventing reverse flow through the conduit means (18) is a check valve (19).

3. A drive circuit as defined in claim 2 in which a. the motor (11) is reversible; and

b. the second control valve (27) has a third position in which it closes the unloading path for the second pump and connects the first and second motor ports (11a, 11b) with the reservoir (14) and the second pump (13), respectively.

4. A drive circuit as defined in claim 2 in which the second pump (13) is connected with the second control valve (27) via a passage in the first control valve (21) which is open in both of said positions of the first tral position, valve. b. a second position (L) in which it sets the first valve 5. A drive CiICUit as defined in claim 4 in which the (21) to second position and the second valve (27) two control valves (21, 27) are sliding plunger units into neutral position, Corporated in a Common valve body having s c. a third position (M) in which it sets the first valve Shaped coring 78, which defines an p cell (21) to neutral position and the second valve (27) ter unloading path for the second pump (13) when to second position both valves are in neutral position.

6. A drive circuit as defined in claim in which the second pump (13) has the greater capacity. 0

7. A drive circuit as defined in claim 2 in which both control valves (21, 27) are operated by mechanism employing a common actuating lever (36), the lever havmg a. a first position in which it sets both valves to neu- 15 tra l position, b. a second position (L) in which it sets the first valve (21) to second position and the second valve (27) to neutral position,

d. a fourth position (F) in which it sets both valves to second position, and

e. a fifth position (R) in which it sets the first valve (21) to neutral position and the second valve (27) to third position.

9. A drive circuit as defined in claim 7 in which a. the control valves (21, 27) are operated by piloted pressure motors (25 and 31, 32); and

b. the common lever (36) positions a pair of pilot valves (35, 35a) which selectively pressurize and vent the piloted pressure motors of the first and c. a third position (M) in which it sets the first valve control 2 7 i l x 21 to position and the Second valve (27) 10. A drive circuit as defined in claim 8 in which to second position, and a. the control valves (21, 27) are operated by piloted d. a fourth position (F) in which it sets both valves to Pressure mOtOrS and and second position. b. the common lever (36) positions a pair of pilot 8. A drive circuit as defined in claim 3 in which both 25 valves which Selectively pressurize and control valves are operated by mechanism employing vent the piloted pressure motors of the first and a common actuating lever (36), the lever having second control valves (21, 27), respectively.

a. a first position in which it sets both valves to neu- 

